The police have just 14 days to issue a 'notice of intended prosecution' (which, in most cases, actually results in a fixed penalty) in certain cases covered by criminal law.
However, parking violations on a public car park have never constituted a criminal offence. (Minor on-street parking violations have now also been decriminalized in those areas where the local authority has taken over control of parking from traffic wardens and the police). Such violations create a civil debt (i.e. if you don't pay it, you can be sued but you can't be hauled before the magistrates) and, as such, are covered by civil law where the 14-day time limit does not apply.
Chris